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Voltage Drop at Breadboard
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Jwillis:

--- Quote from: tggzzz on March 21, 2019, 09:24:32 pm ---
--- Quote from: Jwillis on March 21, 2019, 07:05:18 pm ---I did an experiment to find the resistance of of a bread board compared a piece of wire and trace of a PCB.Its a simple test with a moderately priced mOhm meter , a typical inexpensive 170 mm breadboard with 145 mm rails , 145 mm of AWG 26 wire (typical breadboard wire I use) and 145 mm 1mm wide trace of 1oz PCB.This was done at or as close as possible to the same temperature of 20 C. And Zeroing calibration was done between each test.
The results were not really surprising but interesting non the less .The bread board 145mm rail had a resistance of 46.5 mOhms .The 145mm  26AWG wire had a resistance of 40.2 mOhms . Trace 1mm on the 1 oz PCB showed a 120 mOhm resistance.

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And what was the variation in the resistance (a) with different (diameter, oxidation, dirt) wires (b) with different holes (c) when something was dropped nearby on the bench (d) tomorrow?

Often the absolute value isn't too important, but stability and predictability is important. I would expect soldered joints to be significantly better in that respect.

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Indeed its a static experiment .It wasn't meant to include other unforeseen variations as you describe.But it does have conclusive evidence that the rails resistance is not much more than a piece of wire yet much less than a PCB .Breadboards are not intended to be used as a final construction and I would agree that they have their own inherent draw backs .But soldering ,desoldering and resoldering over and over can have its own inherent draw backs as well .Component damage and wasted resources being at the top. Bread boards ,as mentioned before, have been used for years and years for experimentation prior to prototyping.Although today there are simulators but they have limitations as well like variations in component performance that may not seem apparent until a rough mock-up is put to a test. 
If some feel that the use of a breadboard is not in their best interest for experimentation so be it.The majority list them as one useful tool essential to experimentation.But like any tool proper use and maintenance  is important as well.
   
rdl:

--- Quote from: Jwillis on March 21, 2019, 07:05:18 pm ---I did an experiment to find the resistance of of a bread board compared a piece of wire and trace of a PCB.Its a simple test with a moderately priced mOhm meter , a typical inexpensive 170 mm breadboard with 145 mm rails , 145 mm of AWG 26 wire (typical breadboard wire I use) and 145 mm 1mm wide trace of 1oz PCB.This was done at or as close as possible to the same temperature of 20 C. And Zeroing calibration was done between each test.
...

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Your measurements are not too different from mine, yet the op was seeing more than an order of magnitude higher voltage drop. It seems there almost has to be something not right with either his board or the connections.

Jwillis:
More information on the step down converter might help. I would guess that its not preforming as required.Although so many amps may be supplied to it does not mean that's what you'll get out.Even small amounts of resistance can cause voltages to drop out when theirs not enough current supplied.Any circuit will only draw as much current it requires .But if the current isn't there the voltage will drop. 
tooki:

--- Quote from: rdl on March 22, 2019, 01:46:38 am ---Your measurements are not too different from mine, yet the op was seeing more than an order of magnitude higher voltage drop. It seems there almost has to be something not right with either his board or the connections.

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Definitely. As I said earlier, I've got a few chinesium breadboards that have several ohms (!) contact resistance. (And many more that are just fine, in the dozens of mOhms like yours.) I've marked the bad ones. They're OK for really simple stuff like testing LEDs, but I don't use them for any real circuits. I suspect the OP has a similar issue.

Additionally, some of those chinese "dupont" jumpers have poor connections or wire, and have excessive resistance, too.
Ian.M:
Can you test your crappy chinesium breadboards with a magnet?  It would be interesting to find out if the problems with them are due to the use of steel contact strips.
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